Three-Dimensional Profiling Reveals Trace Metal Depositional Patterns in Sediments of Urban Aquatic Environments: A Case Study in Vancouver, British Columbia, Canada

Abstract

The objectives of our study were to (1) determine the concentrations of zinc, copper, cadmium, and lead in sediments of three different aquatic environments within an urban setting, a wetland, an estuary, and a marine harbor and (2) through a comparison of the concentrations and patterns of metal deposition among the three systems, assess both the historical and current sources of these trace metals to each of these environments. Such information is essential for the proper rehabilitation of these systems. To meet these objectives, we applied a three-dimensional mapping approach which allowed us to spatially visualize the extent of metal contamination within each of the urban aquatic environments. Such an approach proved useful in identifying the trace metal “depositional footprint” for each aquatic system. For the wetland, a creek which flowed into the wetland provided the primary source, for the estuary, the creek which fed the estuary, and a sewer outfall, and for the marine embayment, boat hull cleaning activities and two sewer outfalls were primary sources. Concentrations of metals ranged several orders of magnitude among the three aquatic systems; zinc, 2.5–709; copper, 7–3,667; lead, 4–698; and cadmium, 0.2–4.6 μg g−1 dry weight of sediment. The greatest range was for copper with the point source of copper-based antifouling paints contributing to the maximum concentrations determined for the three aquatic systems. All metals were significantly elevated in surficial sediments in all three ecosystems with recent accumulations of copper exceeding the probable effects level as recommended by the Canadian Council of Ministers of the Environment. It is most likely the primary source of this copper is from the abrasion of tires and brake pads. In the rehabilitation of these systems, attention will have to be paid to the dredging and proper disposal of sediments that have accumulated metals over time, especially those of copper that pose a toxicological concern to aquatic life. It is recommended that Canada as is being done in various jurisdictions in the USA as well as in Europe, pass legislation prohibiting the use of copper in brake pads.